The present invention relates to a positive resist which is used for manufacturing semiconductor devices and to a method for forming a pattern of the positive resist on a substrate.
When the conventional wet etching method is adopted in fine processing involving a pattern dimension of less than several microns as in the case of ICs and LSIs, the amount of undercutting cannot be ignored in relation to processing precision. Therefore, the dry etching method is more widely adopted because of its anisotropic etching without under cutting. Due to this trend, it is important that the resist material used for such fine processing has the resistance to dry etching so as to suppress the thickness reduction of the resist film under the dry etching atmosphere and to prevent the pattern deformation.
Both the resistance to dry etching and the sensitivity to radiation of the positive resist material are correlated with the tendency to dissociate the main chain of the polymer constituting the resist. Since these two properties have opposite tendencies, a positive resist material which satisfies the requirements for both of these properties therefore has not been realized. At the current stage, we must select between a positive resist material which has high sensitivity to radiation but which has low resistance to dry etching, and a positive resist material which has high resistance to dry etching but which has low sensitivity to radiation.
Polyphenylmethacrylate, polybenzylmethacrylate or the like, which is polymethacrylate having a benzene ring as the side chain, is known to have high resistance to dry etching because of its shield effect. However, these substances have low sensitivity to radiation with electron beam or X-ray because of these low G-Value for main chain scission. In addition, these substances have a smaller change in the dissolution ratio in a developer with changes in the molecular weight. Therefore, when a high-sensitivity developer which uses a good solvent with a greater tendency to dissolve the resist is used, resolution is degraded, resulting in low sensitivity.
For example, polyphenylmethacrylate is reported to exhibit a sensitivity of 155 .mu.C/cm.sup.2 (see "H. Saeki, 39th meeting of the Japan Soc. of Appl. Phys. 3a-E-7, P92 (1978)"). The sensitivity mentioned is lower than that of PMMA.